Aluminum-Manganese Recrystallization Barrier

Manganese in aluminum wrought alloys prevents the material from recrystallizing too easily during annealing. The grain stays finer and the alloy more stable. When welding, this means: you have to be careful not to introduce too much heat, otherwise you'll get coarse grain in the heat-affected zone and the strength will suffer. Keep the weld narrow and don't let the part cool down unnecessarily slowly. If you lay the weld cleanly and controlled, the structure remains usable and you won't get cracks.